Magnetic sense in the Japanese eel, Anguilla japonica, as determined by conditioning and electrocardiography

Abstract

SUMMARY Magnetosensitivity of the Japanese eel, Anguilla japonica, was examined by conditioning and electrocardiography. Marine eels, river eels and farmed eels were conditioned to an imposed magnetic field ranging from 12 663 nT to 192 473 nT parallel to the fish body, which was placed along the earth's west-east axis. Electrocardiograms were recorded with electrodes placed close to the fish body inside a PVC pipe shelter. After 10-40 conditioning runs, all the eels exhibited a significant conditioned response (i.e. slowing of the heart beat) to a 192 473 nT magnetic field and even to a 12 663 nT magnetic field, respectively equivalent to 5.92× and 0.38× the horizontal geomagnetic field (32 524 nT) at our laboratory. The west-east vector of the imposed magnetic field (12 663 nT) combined with that of the geomagnetic field and produced a horizontal resultant magnetic field of 21° easterly. Therefore, Japanese eel are magnetosensitive whether they are at sea, in the river or in the farm. Results of the present study were compared with those of past studies that showed no magnetic sense in the American eel, Anguilla rostrata, and the European eel, Anguilla anguilla.